1. Field of the Invention
This invention relates to a method for manufacturing an optical fiber that is optically connected with an optical element used in optical communication, optical measurement and so forth which is held in a housing of an optical communication module. More particularly, this invention relates to an optical fiber manufacturing method which can simply manufacture an optical fiber in which a bare-fiber peripheral surface exposed by removing a resin cover has been coated with a metal and a bare-fiber end has been end-face-treated.
2. Description of the Related Art
Optical communication modules in which optical elements are held in housings have a hermetically sealed structure for making the interior of each housing shut off from the outside, in order to prevent the optical elements from being broken because of moisture condensation or the like.
On this hermetically sealed structure, many methods have ever been proposed and put into practical use. For example, a method is employed in which, as shown in FIG. 2, when a metallic sleeve 1 is used to insert therethrough an optical fiber 10 with resin covering to the interior of a housing 20 of an optical communication module, a resin cover 11 is removed at the part corresponding to a through-hole of the metallic sleeve 1 to make a bare fiber 12 of the optical fiber 10 exposed, where the surface of the bare fiber 12 thus exposed is coated with a metal, the bare fiber 12 is sealed with a solder 2 at the part coated with a metal, and the metallic sleeve 1 is further attached to the housing 20 of the optical communication module with a solder 3 or by seam welding. A method is also employed in which, without use of the metallic sleeve 1, the bare fiber 12 at its part coated with a metal is inserted to the through-hole provided in the housing 20 of the optical communication module, and the bare fiber 12 is directly attached to the housing 20 with a solder to seal up the latter.
Also employed as a method for achieving optical joining between an optical element (not shown) held in the housing 20 and the optical fiber 10, a method is employed in which an end face of the bare fiber 12 exposed by removing the resin cover 11 of the optical fiber 10 is subjected to polishing.
Incidentally, as to a method for fastening the optical fiber 10 to the interior of the housing 20 of the optical communication module, a method is employed in which an end face of the bare fiber 12 exposed by removing the resin cover 11 is polished and this bare fiber 12 is passed through a capillary 4 made of a synthetic quartz glass or a metal, and fastened with an adhesive or by soldering, which is also optically adjusted to the optical element, and thereafter the capillary 4 is fastened to the interior of the housing 20 of the optical communication module. A method is also employed in which the bare fiber 12 is fastened to the capillary 4 and an end face of the bare fiber 12 is polished, which is also optically adjusted to the optical element, and thereafter the capillary 4 is fastened to the interior of the housing 20 of the optical communication module.
In the optical fiber in such a module hermetically sealed with a solder in this way, the bare fiber 12 exposed by removing the resin cover 11 has been coated with a metal on its peripheral surface as described above and also the end face of the bare fiber 12 has precisely been polished (end-face-treated) in order to secure optical connection to the optical element.
Now, where the peripheral surface of the bare fiber 12 is provided with no resin cover, the end face treatment for the bare fiber 12 can be carried out with ease by means of an existent optical-fiber cleaver which applies cleavage cutting. Accordingly, as to the end face treatment for the bare fiber 12, manufacturing operation can be made simple if the treatment making use of the optical-fiber cleaver can be employed without employing the above polishing.
However, in the above optical fiber whose bare fiber 12 surface has been metal-coated for the purpose of hermetic sealing, an electroless Ni coating layer and an electrolytic Au coating layer for example are formed as a subbing layer and a surface layer, respectively, of the metallic coating, having a layer thickness of about 1 μm to 3 μm as a whole. Hence, where the end face treatment is carried out using the optical-fiber cleaver, it is difficult to make a notch cut (strike mark or blade mark) necessary for cleavage, because the bare fiber of the optical fiber stands protected with the metallic coating, so that its rupture cross-section can not be treated to have a end face shape suited for the light input. There has been such a problem. Even if a end face shape suited for the light input has been obtained, there has also been a problem that the metallic foil (coating fin) that forms at the rupture cross-section of the metallic coating covers the light-incident end face of the optical fiber unwantedly, or that, because of such a rupture cross-section, the metallic coating formed on the bare fiber may come with time to tend to come off.
To solve such problems, as disclosed in Japanese Patent Application Laid-open No. H07-27952, a method is proposed in which, when an optical-fiber bare fiber is treated to provide a metallic coating, a mask material is beforehand used at the part to be cut with an optical-fiber cleaver, or a method in which, after the optical-fiber bare fiber has been treated to provide a metallic coating, the metallic coating is etched away at the part to be cut. Both the methods, however, have had a difficulty that they make manufacturing steps complicate.